False rumors that frighten parents are clearly behind the current outbreak of measles linked to Disneyland, doctors said at a Senate hearing Tuesday.
But they said the attention being focused on the outbreak might turn around a dangerous trend of opting out of vaccines for philosophical reasons.
"It's making people realize the consequences of their choices," Dr. Kelly Moore, director of the Tennessee Health Department's immunization program, said at a hearing of the Senate Health, Education, Labor and Pensions Committee.
"This bell goes off when they hear scary things about vaccines, and it's hard to unring that bell."
More than 120 cases of measles have been reported in the U.S. this year, most of them linked to the Disneyland outbreak, the Centers for Disease Control and Prevention reports.
It's an unusually high number to have so early in the year. Last year, 644 cases of measles were reported in the U.S., the most in 20 years.
"Most of the cases  are from California, and 13 cases are from my community," Dr. Mark Sawyer, a professor of pediatrics at the University of California-San Diego, told the committee. "Most of those infected were intentionally unvaccinated, some of them did not know their vaccination status, and a minority of them were vaccinated."
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In San Diego County, Sawyer said, 3.5 percent of children have been exempted from school vaccine requirements. "We have individual schools in which 30 to 50 percent of the students are not fully immunized," he said.
These pockets give the virus a chance to take hold when it does get imported by a traveler, said Dr. Anne Schuchat, a top expert on vaccines at the CDC.
"We think these micro-communities are making it difficult to control the spread of measles and are making us vulnerable to having the virus re-establish itself in our country again," she said.
That means the Disney outbreak will not be unique, Sawyer said. "Given our current immunization rates, this will happen again," she said.
Moore said worried parents are trying to do their best for their children. "These parents often refuse to vaccinate their children out of fear," she said. Unfounded rumors are making the rounds of Internet chat rooms and blogs and among friends. "This bell goes off when they hear scary things about vaccines, and it's hard to unring that bell."
The good news, Moore said at the hearing, is that focused attention of the media, Congress and doctors is getting the right information out there: Measles can be dangerous, the vaccine is safe and effective, and kids need to get it to protect themselves and their communities.
"It's making people realize the consequences of their choices," she said. "A lot of this can be overcome with credible information from trusted sources."
"It's making people realize the consequences of their choices."
Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, said parents are trying to figure this out on their own, and they don't need to. For instance, many fear that it's somehow too much for a baby to get five or six jabs all at the same time.
"Many parents do mention the number of shots that children get at a particular visit that is something that concerns them," Schuchat said. But the Advisory Committee on Immunization Practices, made up of a variety of experts and sometimes parents, as well, asks and answers the question every year.
"Our Advisory Committee on Immunization Practices reviews the science of the vaccines [and] the diseases and updates the schedule every year based on the best information available," she said at the hearing.
The recommendations are clear, she said: Vaccinate your kids on time.
"While overall measles vaccination coverage rates are high at 92 percent, 1 in 12 children in the United States is not receiving his first dose of measles-mumps-rubella [MMR] vaccine on time, underscoring considerable measles susceptibility across the country," Schuchat said.
States that let parents opt out for philosophical reasons have higher rates of unvaccinated kids than states like Mississippi, which allow only medical exemptions.